1. Field of the Invention
The present invention generally relates to the conversion of chemical energy to electrical energy. More particularly, this invention relates to a novel anode material formulation comprising a carbonaceous material and a lithiated mixed metal oxide, a lithiated metal oxide or a lithiated metal sulfide for the negative electrode of a rechargeable, nonaqueous electrochemical cell. In that respect, the use of graphite and a lithiated metal vanadium oxide as an anode material mixture in conjunction with a cathode active material in a lithium ion electrochemical cell has several advantages. These include increased anode density resulting in higher capacity for the intercalation of lithium, lower initial irreversible capacity, excellent reversibility of lithium doping and undoping, improved cell end of discharge cycle indication, and the prevention of negative electrode copper current collector corrosion prior to initial charging of the cell in comparison to that known by the prior art.
2. Prior Art
The use of lithiated nickel vanadate as an anode material is described by Orsin et al. in Solid State Ionics 1998, 107, 123-133. This lithiated metal vanadium oxide material displays very high initial capacity, but suffers from poor capacity retention upon cycling. In U.S. Pat. No. 5,284,721 to Beard, the use of lithiated metal oxides, where the metal is selected from scandium, titanium, yttrium and zirconium, as an anode material, is described. U.S. Pat. No. 5,545,468 to Koshiba et al. claims the use of LiTi2O4 as an anode for a rechargeable lithium ion cell. Lithiated manganese oxides and vanadium oxides were studied as anode materials by Dahn et al. in J. Electrochem. Soc. 1995, 142, 1742-1746. These materials were used for secondary batteries incorporating aqueous electrolytes. The use of a mixture of graphite and copper oxide or lithiated copper oxide as an anode for lithium ion batteries is also described in U.S. Pat. No. 5,576,121 to Yamada et al. However, copper oxides do not provide as high of capacity as the metal vanadium oxide materials. Nonaqueous lithium primary batteries using metal vanadium oxide additives in the cathode for end of service indication are described in U.S. Pat. No. 5,180,642 to Weiss et al.
The object of this invention is to improve the performance of lithium ion secondary cells. Accordingly, the negative electrode or anode comprises a mixture of graphite or xe2x80x9chairy carbonxe2x80x9d and a lithiated metal oxide, a lithiated mixed metal oxide or a lithiated metal sulfide, and preferably a lithiated metal vanadium oxide. A most preferred formulation is graphite mixed with lithiated silver vanadium oxide or lithiated copper silver vanadium oxide. This anode active mixture produces advantages in lithium ion secondary cells not known in the prior art including the prevention of corrosion of the copper current collector prior to initial cell charging, improved cell end of service indication, high capacity for the intercalation of lithium, low initial irreversible capacity, and excellent reversibility of lithium doping and undoping in the anode electrode.
These and other objects of the present invention will become increasingly more apparent to those skilled in the art by reference to the following description and to the appended drawings.